He ii arises in the innermost BLR close to the innermost part of the accretion disc. Because it takes 54 eV to doubly ionized helium, most of the ionizing photons needed to produce He ii come from close to the Wien cutoff of the spectrum of the accretion disc. This emission from the innermost accretion disc is the most variable part of an AGN's spectrum. He ii comes from ten or more times closer to the black hole than other BLR lines studied (see [1]} for a review of the structure of the BLR). Because of the combination of the small size of the He\(^+\)  emitting region and the rapid, high variability of the relevant ionizing continuum, He ii emission is highly variable. For NGC 5548, He ii variations lag continuum variations by less than a day [2]} rather than the many days or weeks for other broad lines. The He ii lines can only be used as a reddening indicator if the He ii \(\) 1640 and \(\) 4686 observations are near simultaneous. We will propose in Section 5.1 below that the strong variability of He ii can be exploited to overcome the line-blending problem and estimate the \(\) 1640/\(\) 4686 ratio.
